To date, a device that includes an excitation coil wound so as to be electrically insulated and magnetically joined around a magnetic core enclosing conducting wires through which measured currents flow, excitation means that generates a rectangular wave voltage that causes polarity of an excitation current supplied to the excitation coil to invert in accordance with a set threshold value, with the magnetic core in a saturated state or a near-saturated state, and current detection means that detects the measured currents based on a change in a duty ratio of the rectangular wave voltage output from the excitation means, has been disclosed as a current detection device (for example, refer to Patent Document 1). According to this device, there is little effect from ambient environmental conditions, and a wide range of minute current can be detected with a small size and at low cost.